1. Technical Field
The present invention relates to a liquid ejection device which performs power amplification on a drive signal to an actuator ejecting a liquid, and is suitable for a liquid ejection printer which prints characters, images, etc. by ejecting a minute liquid droplet out of a nozzle of a liquid ejection head and forming fine particles (dots) on a printing medium.
2. Related Art
In a liquid ejection printer, an actuator such as a piezoelectric element is provided and a predetermined drive signal has to be applied to this actuator to eject a liquid out of a nozzle of a liquid ejection head. Since this drive signal has a relatively high voltage, it is necessary to perform power amplification on a drive waveform signal serving as a reference of the drive signal by using a power amplifier. Therefore, in JP-A-11-204850, a digital power amplifier which has an extremely small power loss compared to an analog power amplifier and can be made compact is used, pulse modulation is performed on a drive waveform signal by a modulator to obtain a modulated signal, power amplification is performed on the modulated signal by the digital power amplifier to obtain an amplified digital signal, and the amplified digital signal is smoothed by a Lowpass Filter to obtain a drive signal.
However, when the actuator is a capacitive load such as a piezoelectric element, the Lowpass Filter needs a damping resistor because of the absence of a resistance component, resulting in a large power loss due to this damping resistor. That is, as is well known, when a Lowpass Filter is formed of a coil and a capacitor, there is a resonance frequency represented by the inductance L of the coil and the capacity C of the capacitor, and the presence of this resonance frequency makes it possible to store power and attenuate voltage fluctuations corresponding to the modulation frequency. However, resonance sometimes occurs due to the resonance frequency. When a resistance component is present in a circuit, the resonance is suppressed (attenuated) by the resistance component; however, since a capacitive load such as a piezoelectric element has no or an extremely small resistance component, the resonance is not suppressed (attenuated) and remains. To suppress (attenuate) the remaining resonance, a circuit has to be provided with a resistor called a damping resistor for suppressing (attenuating) the resonance, and power is consumed when the damping resistor suppresses (attenuates) the resonance.